Linker error: duplicate symbol only on CI

[dev-ardi]

          ld.lld: error: duplicate symbol: ffi_acme_mail_common_rust_future_free_u16
          >>> defined at lib.rs:43 (mail/mail-common/src/lib.rs:43)
          >>>            /builds/rust/acme-rust/target/debug/deps/proton_mail_common-7cec9c6870e7ff37.dmebg5zwg7p92w3ow7yauihgv.rcgu.o:(ffi_proton_mail_common_rust_future_free_u16)
          >>> defined at lib.rs:43 (mail/mail-common/src/lib.rs:43)
          >>>            acme_mail_common-08ac6ddaf12194af.9lql9jv0btadkdtkwrx2qn7bt.rcgu.o:(.text.ffi_proton_mail_common_rust_future_free_u16+0x0) in archive /builds/rust/proton-rust/target/debug/deps/libproton_mail_common-08ac6ddaf12194af.rlib
          
          ld.lld: error: duplicate symbol: ffi_acme_mail_common_rust_future_poll_i16
          >>> defined at lib.rs:43 (mail/mail-common/src/lib.rs:43)
          >>>            /builds/rust/acme-rust/target/debug/deps/proton_mail_common-7cec9c6870e7ff37.dmebg5zwg7p92w3ow7yauihgv.rcgu.o:(ffi_proton_mail_common_rust_future_poll_i16)
          >>> defined at lib.rs:43 (mail/mail-common/src/lib.rs:43)
          >>>            acme_mail_common-08ac6ddaf12194af.9lql9jv0btadkdtkwrx2qn7bt.rcgu.o:(.text.ffi_proton_mail_common_rust_future_poll_i16+0x0) in archive /builds/rust/proton-rust/target/debug/deps/libproton_mail_common-08ac6ddaf12194af.rlib
          
          ld.lld: error: duplicate symbol: ffi_acme_mail_common_rust_future_cancel_i16
          >>> defined at lib.rs:43 (mail/mail-common/src/lib.rs:43)
          >>>            /builds/rust/acme-rust/target/debug/deps/proton_mail_common-7cec9c6870e7ff37.dmebg5zwg7p92w3ow7yauihgv.rcgu.o:(ffi_proton_mail_common_rust_future_cancel_i16)
          >>> defined at lib.rs:43 (mail/mail-common/src/lib.rs:43)
          >>>            acme_mail_common-08ac6ddaf12194af.9lql9jv0btadkdtkwrx2qn7bt.rcgu.o:(.text.ffi_proton_mail_common_rust_future_cancel_i16+0x0) in archive /builds/rust/proton-rust/target/debug/deps/libproton_mail_common-08ac6ddaf12194af.rlib
          
          ld.lld: error: duplicate symbol: ffi_acme_mail_common_rust_future_complete_i16
          >>> defined at lib.rs:43 (mail/mail-common/src/lib.rs:43)
          >>>            /builds/rust/acme-rust/target/debug/deps/proton_mail_common-7cec9c6870e7ff37.dmebg5zwg7p92w3ow7yauihgv.rcgu.o:(ffi_proton_mail_common_rust_future_complete_i16)
          >>> defined at lib.rs:43 (mail/mail-common/src/lib.rs:43)
          >>>            acme_mail_common-08ac6ddaf12194af.9lql9jv0btadkdtkwrx2qn7bt.rcgu.o:(.text.ffi_proton_mail_common_rust_future_complete_i16+0x0) in archive /builds/rust/proton-rust/target/debug/deps/libproton_mail_common-08ac6ddaf12194af.rlib
          
          ld.lld: error: too many errors emitted, stopping now (use -error-limit=0 to see all errors)
          collect2: error: ld returned 1 exit status

I'm getting a lot of these linker errors.
I have 2 crates, both call uniffi_setup_scaffolding!() (no namespace override)

I get this error in the following cases:

1. cargo build
2. cargo build --profile test (no error) -> cargo test error!
3. both using lld and system linker

Using stable rust 1.82, and this only happens in our CI.

Any ideas would help here, at least to reproduce the issue locally!
cc: #2384